1.
A glowing hole in Whispering Depth, under the Blighted Village. Practically, you have to fight the first spiders and ettercaps before you can get to it. And then it puts you down near the hook horrors. Not recommended.
2.
A concealed area in the Zhentarim Hideout, to the left of the treasure rooms. If the Zhentarim catch you entering, they will fight. The area you land in is safe, but you have to deal with the minotaurs (and traps) to get further.
3.
The mushroom portal near the back area of the Riverside Teahouse. I think this might need to be activated from the other side first. The area is safe except for environmental hazards.
4.
The Defiled Temple, through the puzzle room. The area you land in is safe, but you have to deal with the minotaurs or the bulette to get out. (And the temple's own defenses.)